This invention relates to a fish and/or particulate screen and more particularly to a so-called xe2x80x9cbarrel typexe2x80x9d fish and/or particulate screen. Specifically, a barrel type fish and/or particulate screen is disclosed having constant water approach velocity at substantially all mesh points on the barrel screen despite wide variations in flow volume through the fish and/or particulate screen.
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A critical feature of a fish and/or particulate screen is the water approach velocity. The lower the water approach velocity, the more fish and/or particulate-friendly the screens become, but also the more costly they become because of sheer size.
The barrel type fish screen is a known fish screen device. In the typical barrel type screen, a cylindrically arrayed mesh, usually a metallic screen having a minimum mesh size, is used to protect juvenile fish by preventing fish passage through the mesh of the screen.
Barrel type fish screens include cylindrically arrayed mesh defining an enclosed interior. The mesh confines the fish and/or particulate matter to the exterior of the cylinder. Water is withdrawn from the enclosed interior of the mesh at one of the circular ends of the cylindrically arrayed mesh.
The reader will understand that the mesh utilized with such screensxe2x80x94including the screen disclosed hereinxe2x80x94can vary. We prefer perforated plate arrayed over a cylindrical body in the form of a stressed skin. Additionally, mesh can be defined by woven wire such as a wire screen. Alternately, so-called xe2x80x9cwedge wirexe2x80x9d can be used. This wedge wire defines smaller exterior openings expanding to larger interior openings. Such wedge wire has the property that lodging of particles within the mesh is inhibited. Mesh can also be made from a fabric arrayed about a cylindrical body. In the following specification, we use the term xe2x80x9cmeshxe2x80x9d to include these and other equivalent options.
Unfortunately, withdrawal of water at a chosen flow rate from one end of the cylindrically arrayed mesh results in non-uniform velocity (or velocity head) through the mesh. In the usual case, the non-uniform velocity is small away from the point of water withdrawal and high adjacent the point of water withdrawal from the closed interior of the cylindrical mesh.
Withdrawal of water at a different flow rate from one end of the cylindrically arrayed mesh results in a different non-uniform velocity (or velocity head) through the mesh. As the flow rather changes, it will be expected that the non-uniformity of the velocity (or velocity head) will likewise change. Thus, conventional barrel type fish and/or particle screens are subjected to non-uniformity of flow rate through the screens, this non-uniformity of flow rate being generally aggravated as overall flow rate changes through the screen.
Complicating these issues of non-uniform velocity through the mesh for a single flow rate and changing non-uniformity velocity through the mesh for different flow rates is the requirement that mesh must be sized for different fish species and have a minimum flow rate for different fish species. For example, there are times in the Central Valley estuary of California when delta smelt are in the water require a maximum approach velocity of 0.2 feet per second is advisable through mesh defining maximum openings of {fraction (3/32)}nds of an inch. When only salmonids are present, it is possible that the permitting agencies will allow an approach velocity of 0.33 feet per second through mesh of the same size. If cleaning procedures for the cylindrical mesh are intermittent in nature, an approach velocity may be required as low 0.0825 feet per second. This low velocity is required because of the accumulation of particulate in the defined apertures within the mesh.
If the mesh is intended to preclude or reduce the passage of particulate, non-uniform velocity distribution through the mesh can result in progressive clogging. Initially, the mesh will become partially obstructed. Flow will stop at one portion of the mesh; flow velocity will increase at the remaining unblocked mesh. Thus the presence of clogging particulate in the water can progressively clog the mesh, starting at xe2x80x9chot spotsxe2x80x9d with mesh apertures of initial high velocity (or velocity head). As a rough approximation, such clogging seems to vary with the square of the flow velocity flowing through the mesh being clogged.
Additionally, when a fish screen is operating to protect fish from being transported with water from one water body to another (such as a pump or siphon), the flow rate across the fish screen between the supplying and receiving waters must frequently vary. These variations can occur with pump intake velocity change, tidally and/or with river stage variation. For example, where such a barrel type fish screen is used on a siphon between an elevated river and a lower receiving reservoir, the flow rate across the fish screen will vary as the reservoir fills. Even with the use of flow modulating valves and pumps, variable flow rates complicate the water approach velocity issue. In all fish screens of which we are aware, flow volume variations occurring along the designed screens result in non-uniform flow flow if rates through the screens.
U.S. Pat. No. 6,051,131 issued to Maxson Apr. 18, 2000, discloses a cylindrical intake screen to prevent damage to fish and other aquatic organisms by providing a controlled velocity profile at a particular flow rate. By extending two or more concentric tubular flow modifiers into one end of the screen, it is possible to achieve flow uniformity of more than 90% at a chosen flow rate.
This device does not consider wide variations of flow rates due to changing velocity head and flow volume requirements.
In the following, the fish screen will be illustrated with respect to a siphon. It will be understood that use with various valving schemes and pumps are contemplated. Additionally, this screen can be used with particulate matter as well.
A barrel type fish and/or particulate screen includes mesh over a supporting cylindrical framework. The cylindrical mesh is closed at both ends and defines an interior that can only be accessed through the mesh. One closed end opens to a fluid withdrawal conduit, which is connected to an outlet such as a pump inlet or a siphon. An inner, substantially conical withdrawal manifold is provided with the base of the substantially conical withdrawal manifold connected to the withdrawal conduit and the manifold extending substantially the axial length of the cylindrical mesh. The preferred embodiment of the substantially conical withdrawal manifold is a right cylindrical cone of constant pitch. This right circular cone extends the full length of the barrel type fish and/or particulate screen from the withdrawal conduit at the base of the cone. The conical withdrawal manifold is typically truncated at its end and supported at the closed circular end of the mesh cylinder opposite from the withdrawal conduit. To provide for optimum constant flow through the metal mesh, the generally conical manifold can be formed of a series of connected and truncated cones with increasing conical pitch away from the withdrawal conduit. In the ultimate progression, these connected and truncated cones if continuously and asymptotically combined will result in a paraboloid edge to what is otherwise a substantially conical structure. In all cases, the substantially conical withdrawal manifold defines uniformly sized and arrayed flow apertures. These flow apertures have the same unit area per unit length of the substantially conical withdrawal conduit. This same unit area per unit length produces within the withdrawal manifold, a substantially constant velocity or velocity head distribution at all cross-sections of the manifold taken normal the flow along the major axis of the conical shape. Flow velocity head through the mesh is maintained uniformly distributed at all changes of flow rate through the barrel screen device.